Post-traumatic stress disorder (PTSD) is a serious psychiatric condition that affects a substantial number of military personnel who served in Afghanistan and Iraq. Over 30% of all OEF/OIF/OND Veterans who receive health care from the VA have been diagnosed with PTSD. The disorder is characterized by symptom clusters of re-experiencing or intrusion, hyperarousal, avoidance, and negative alterations in cognition. In addition to these distressing emotional and mood problems, impairments in attention and executive control can be observed. Impairments in these frontal lobe functions could, in turn, have a negative impact on social and occupational activities. Recent studies show that PTSD is associated with deficits in highly specific frontal lobe functions, such as response inhibition and sustained attention. These cognitive deficits are strongly correlated with symptom severity. Conversely, other executive control processes, including interference resolution and error monitoring, are intact. Little is known about why these dissociations occur, and what their underlying neural mechanisms might be. The current project will extend previous findings in the OEF/OIF Veteran population by asking why this specific pattern of spared and impaired frontal lobe functions is observed, and how targeted task manipulations such as cues and rewards might improve performance. The proposed studies will investigate the cognitive and neural mechanisms of three cognitive domains that are difficult for Veterans with PTSD: (1) staying ?on task?, the ability to focus on the task at hand without mind wandering; (2) response inhibition, the ability to withhold inappropriate motor responses; (3) distractor resistance, the ability to filter out extraneous stimuli to maintain items in working memory. The project will use a direct measure of the brain's electrical activity to determine when in the information processing stream potential weaknesses occur. This is a critical element, because knowing if a particular deficit is associated with early suppression of distractors, sustained attention, and/or response inhibition may inform future therapeutic approaches. The project will also record electroencephalographic (EEG) activity at rest to examine possible changes in connectivity associated with PTSD. The relationship between off-task cognition (?mind wandering?), fluctuations of attention, and trauma-related thoughts and memories will be explored. The proposed studies will contribute to larger efforts to characterize this Veteran population by including PhenX common data elements and easily replicated methods that can be implemented at other research sites. An innovative aspect of the current proposal is its novel approach to resting state EEG, which is easier and less expensive to collect than resting state fMRI. The observed patterns of EEG network activity will be related to specific ?phenotypes? of resting state cognition as determined by the validated Amsterdam Resting-State Questionnaire (Diaz et al., 2013, 2014). We hope the project will lead to broader efforts to characterize the brain states correlated with maladaptive thoughts in a naturalistic setting, with possible use of this knowledge in the future to predict clinical response to treatment.